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Abstract
Objective Basilar trunk perforator (BTP) aneurysms are rare. Treatment options traditionally considered for these uncommon lesions have included direct surgery, endovascular therapy, or conservative management. Flow diverters represent a newer therapeutic option for BTP aneurysms but pitfalls and complications are unknown. We describe three patients with BTP aneurysms treated with flow diverter stents.
Methods All three patients had ruptured BTP aneurysms and, after loading doses of dual antiplatelet agents, underwent treatment with a flow diverter alone (two patients) or in combination with an intracranial stent (one patient).
Results Complications directly (two thromboembolic events) or indirectly (one hemorrhage at the external ventricular drain site, probably facilitated by the dual antiplatelet therapy) occurred in all three patients and resulted in permanent morbidity in one case. Imaging follow-up confirmed obliteration in all three patients, and no episodes of rebleeding from the aneurysms were observed at follow-up.
Conclusions Flow diverters are effective in obliterating BTP aneurysms. However, given the challenges and complications encountered, especially in patients with ruptured lesions, their use must be carefully weighed against other available therapeutic modalities, including observation.
- Aneurysm
- Flow Diverter
- Hemorrhage
- Technique
- Subarachnoid
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Introduction
Basilar trunk perforator (BTP) aneurysms are exceedingly rare vascular lesions of the posterior cerebral circulation. These aneurysms are probably dissecting in nature and may represent a diagnostic quandary as they can be missed on the initial angiogram.1 Regardless of the therapeutic approach utilized in their treatment (open surgery or endovascular therapy), their management is very challenging. Two main subtypes of BTP aneurysms are recognized: one type arises adjacent to the main basilar trunk and another type arises directly from a perforating pedicle but more distal from its origin.2 These aneurysms originate from very small vessels generally considered unsuitable for endovascular navigation. Because of their very small size, their most likely dissecting nature, and their unfavorable neck geometry, direct coiling is usually not safe or feasible. Thus direct surgery or even conservative treatment has been advocated.3 The advent of flow diverters (FDs) provides a potential valid alternative for the treatment of these challenging aneurysms, as recently reported in a single case report.4 In this report, we describe a series of three patients with BTP aneurysms treated with FDs.
Material and method
We retrospectively analyzed the records of three patients with ruptured BTP aneurysms treated with flow diversion. Demographic, clinical, and radiological data of these patients are summarized in table 1.
Present study case series
Table 2 provides a summary of all of the cases of BTP aneurysms reported in the literature treated with various endovascular techniques.
Cases of ruptured basilar trunk perforator aneurysms managed with endovascular techniques reported in the literature
Illustrative cases
Case No 1
A middle-aged patient presented with sudden severe headache and was found to have a Fisher grade 4 subarachnoid hemorrhage (SAH) with extension into the fourth ventricle (figure 1) and no apparent vascular abnormality on CT angiography.
Head CT scan was performed on admission, showing a perimesencephalic subarachnoid hemorrhage and blood in the fourth ventricle.
Digital subtraction angiography (DSA), performed the day after the ictus, showed a small (1.5 mm) aneurysm arising from the proximal portion of a rostral basilar artery perforating vessel (figure 2). After a multidisciplinary discussion of the case, it was decided to pursue endovascular treatment. The patient was premedicated with acetylsalicylic acid (ASA 500 mg) and Plavix (400 mg). Under general anesthesia and after administration of an intravenous bolus of 3000 IU of heparin, a 6 F Envoy guiding catheter (Cordis Neurovascular) was placed in the left vertebral artery. A Marksmann microcatheter was then navigated over a Transed EX Soft Tip microguidewire (Stryker) to the right P1 segment. A pipeline embolization device, 3×16 mm, was placed from the right P1 to the basilar artery (figure 3), bridging the site of origin of the aneurysm. Immediate control DSA showed persistent filling of the aneurysm and slower filling of both superior cerebellar arteries for which an intravenous infusion of 20 mg abciximab was administered.
Cerebral digital subtraction angiography performed on day 1 post-subarachnoid hemorrhage showed a small 1.57 mm aneurysm filling next to the upper third of the basilar artery without an apparent relation to the latter.
Cerebral digital subtraction angiography. Flow diverter released in the basilar artery across the origin of the basilar trunk perforator (BTP). Note how the BTP aneurysm is still filling.
The immediate postoperative course was uneventful and dual antiplatelet therapy (Plavix 75 mg/daily and ASA 300 mg/daily) was administered. A repeat DSA 7 days later showed persistent filling of the aneurysm and no parent artery compromise (figure 4). However, on SAH day 14, the patient suffered a sudden onset of hemiplegia, and brain MRI revealed a well delimited ischemic area at the ponto-mesencephalic junction ipsilateral to the aneurysm, likely due to the occlusion of the basilar perforator (figure 5). DSA on the same day showed no filling of the BTP aneurysm (figure 6). Six months later, the patient continues to have a slight monoparesis of the upper extremity (modified Rankin Scale score of 2).
Cerebral digital subtraction angiography on day 8 after flow diverter deployment. The basilar trunk perforator aneurysm is still evident. Neurological condition has remained stable to date.
Brain MRI performed after sudden appearance of left hemiplegia. On the left, diffusion weighted imaging sequence shows the presence of a circular hypersignal at the level of the right ponto-mesencephalic junction, highlighted with a yellow cross. On the right, vascular reconstructions demonstrated the occlusion site at the level of the aneurysmatic perforator, evidenced with a yellow cross.
Control cerebral digital subtraction angiography. The aneurysm was no longer visible. A basilar trunk perforator occlusion was supposed on the basis of both neurological condition and radiological findings.
Case No 2
A patient in his/her sixties presented with severe sudden headache and third cranial nerve palsy (World Federation of Neurological Surgeons score 2). CT scan of the head showed a Fisher grade 4 SAH (figure 7A). CT-angio and two consecutive DSA recordings did not reveal any vascular abnormality (figure 7B). A third DSA, performed because of a strong suspicion of an aneurysmal source, showed a very small (1.2 mm) right-sided BTP aneurysm arising from the proximal portion of a rostral basilar artery perforator.
(A) Head CT scan was performed on admission showing a diffuse subarachnoid hemorrhage. (B) The first two digital subtraction angiography recordings did not demonstrate any vascular abnormality.
It was decided to treat the aneurysm with endovascular therapy. After premedication with ASA (500 mg) and Plavix (600 mg) the patient was placed under general anesthesia. A bolus of 3000 IU of heparin was administered intravenously, and a 6 F Envoy guiding catheter (Cordis Neurovascular) was placed in the left vertebral artery. An Enterprise stent (Codman 4.5–14 mm) was deployed through a Prowler microcatheter (Codman) in the basilar artery, bridging the perforator harboring the aneurysm. As the aneurysm continued to fill after stent deployment, a Silk (Balt 3.5–25 mm) FD was placed within the Enterprise stent. However, immediate thrombosis of the device was noted which was reversed with intravenous tirofiban (44 mL/h for 30 min followed by 11 mL/h for 24 h) with complete revascularization (figure 8).
(A) On a third attempt at digital subtraction angiography, a small circular formation was filling next to the upper third of the basilar artery without any apparent relation to the latter. (B) A stent Enterprise 4.5×14 mm (Codman) was released but the aneurysm was still filling. (C) An overlapping flow diverter Silk 3.5×25 mm (Balt) was released. (D, E) Periprocedural in-stent thrombosis treated with intravenous tirofiban with optimal results.
Follow-up DSA was performed 24 h later confirming complete recanalization and no residual aneurysm filling (figure 9A). One week after treatment, the third cranial nerve palsy had completely recovered and the patient was discharged home with no other deficits (modified Rankin Scale score of 0). Follow-up MRI after 3 years did not show any vascular abnormality (figure 9B).
(A) Control cerebral digital subtraction angiography on day 1 after flow diverter (FD) release, showing the patency of the vertebrobasilar system along with the two overlapping FDs. Note that the basilar trunk perforator aneurysm is no longer visible. (B) Control angio-MRI performed 3 years after discharge did not show any vascular abnormality.
Discussion
We have reported three patients of BTP aneurysms treated with flow diversion. BTP aneurysms are rare lesions. Depending on their location on the basilar trunk, they are classified as caudal, middle, or rostral,6 although most BTP aneurysms are middle or rostral. These aneurysms are characteristically very small, share a dissecting etiopathogenesis, and show delayed filling on catheter angiography due to slow flow. These features explain why BTP aneurysms can be very difficult to see, even with modern high resolution three-dimensional angiography. On head CT, 50% of BTP aneurysms present with a focal subarachnoid bleed limited to the basal cisterns (premesencephalic or prepontine),7 while the remaining present with a diffuse SAH pattern. The first catheter angiography investigation may not show the lesion in up to one-third of patients, with the lesion becoming evident only on repeat or even on the third DSA (as shown in our case Nos 2 and 3).
Treatment of BTP aneurysms is a therapeutic challenge. In a review of published cases,8 10 patients underwent surgical treatment (consisting of clipping or trapping), three patients underwent endovascular treatment favored by parent arteries large enough to allow for safe microcatheterization, while the remaining three patients were managed conservatively with spontaneous ensuing thrombosis of their very small BTP aneurysms (1 mm). Direct coiling of BTP aneurysms is rarely possible because it requires catheterizing exceedingly small caliber perforators often arising at a straight angle from the basilar trunk. Moreover, the very small size of these aneurysms precludes safe coil placement. For these reasons, some operators have recently explored the possibility of using multiple intracranial stents to provide enough of a flow diversion effect to promote aneurysm obliteration.5 ,9
The introduction of FDs in clinical practice provides a newer and potentially more effective therapeutic method to treat BTP aneurysms. Recently, Chalouhi et al10 reported the first successful use of an FD to treat a ruptured BTP aneurysm:11 a PED was deployed in the basilar artery of an elderly patient to treat a ruptured 1.5 mm BTP aneurysm. This was followed by intra-aneurysmal thrombosis with preservation of parent artery patency. As BTP aneurysms occur in a straight segment of the vessel, shorter FDs are required which decreases the coverage of the uninvolved perforators. Additionally, less ‘manipulation’ of the microcatheter and the device is required during deployment in order to get adequate apposition against the parent artery wall as opposed to a more tortuous segment, such as the paraclinoid internal carotid artery.
Shortcomings of endovascular stents and FDs for BTP aneurysms include the risk of thromboembolic complications12–16 and the need for dual antiplatelet therapy. With growing experience and increasing application of FDs, several series and case reports have stressed the danger of periprocedural as well as delayed thromboembolic complications, especially when using FDs in the posterior circulation.17 ,18 Indeed, our case series suggests that caution must be applied when applying this novel strategy to BTP aneurysms. One of our patients suffered from perforator occlusion with non-disabling persistent neurological deficit, and another suffered in-stent thrombosis immediately reversed with intravenous pharmacological therapy without clinical sequelae. Moreover, the last patient suffered a hemorrhage (potentially facilitated by the dual antiplatelet therapy) along the external ventricular drain tract requiring surgery for hematoma evacuation. Another limitation of FDs in the setting of acute SAH is the risk of rehemorrhage during the latency interval before occlusion of the aneurysm occurs. This may be less of an issue for BTP aneurysms which, as previously indicated, may have a more benign natural history and hence a lower risk of rebleeding. Similarly, the risk of delayed stenosis within the device at follow-up remains unknown and requires long term monitoring and follow-up of these patients.
Conclusion
In conclusion, we have reported three patients recently treated at three different institutions with flow diversion for ruptured very small BTP aneurysms. All three patients suffered complications directly or indirectly related to the treatment. Although flow diversion may represent an appealing and theoretically valid therapeutic strategy for these aneurysms, caution must be applied in their widespread application. When treating physicians are faced with patients with ruptured BTP aneurysms, all possible options, which include surgery, endovascular therapy, and potentially observation, must be carefully considered.
References
Footnotes
Contributors SP and AC: guarantors, conception of the study, drafting of the article, and final approval of the version to be published. DC, MR, NB, and GP: design of the data collection, drafting of the article, and final approval of the version to be published. LV and GL: interpretation of the radiological results, revision of the article, and final approval of the version to be published.
Competing interests GL: consultancy for ev3/Covidien (money paid to the institution); consulting fee or honorarium from Codman/Johnson and Johnson.
Patient consent We ensure the complete anonymity of patients in this study.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Additional documentation from this study is available on request to the corresponding author.